The invention concerns, in a first aspect, an arrangement for determining the relative position of two bodies which are movable in relation to each other. On a first body of the two, a separate measuring tape is arranged which features at least one track of measuring markings, distributed along the length of the tape. The second of the two bodies carries a sensor arrangement which responds to the measuring markings and which, in the course of relative movement between the two bodies, travels along the track.
In general, one seeks to keep the measuring tape free of folds or distortions so that the accuracy of measurement is not impaired by unevennesses of the measuring tape, and so that, if the second body brushes closely over the measuring tape, the second body""s motions are not hindered by undulations in the measuring tape. Occasionally, the position-determining arrangement is used in a working environment which is subject to relatively strong variations in temperature. Such variations in temperature may occur simultaneously over the entire position-determining arrangement, or may only occur locally on individual points of the position-determining arrangement. Differences in the heat-transfer conditions and/or differences in thermal-expansion conditions between the first body and the measuring tape can cause, if the temperature of the working environment drops, the first body to contract more quickly and/or more strongly as a function of temperature than the measuring tape. This may occur, say, if the first body is made of a highly heat-conducting metal, while the measuring tape consists of a material which is thermally significantly less conductive. The consequence of such a drop in temperature could cause a distortion in the measuring tape, if the latter cannot accompany the thermal contraction of the first body fast enough.
Consequently, it is an object of the invention in its first aspect to provide a way that makes it possible to avoid or at least reduce distortions of the measuring tape, even under temperature variations of the working environment.
Such object is achieved, in accordance with the invention, by attaching the measuring tape to the first body at at least two points of attachment, arranged at a distance from each other along the longitudinal direction of the tape. Between the points of attachment, the measuring tape is elastically stretched in the longitudinal direction of the tape. The elastic stretching of the measuring tape creates a region in which the measuring tape will follow a thermally caused contraction of the first body and will also be able to contract, without losing its smoothness. In this fashion, unevennesses can be avoided, even in those cases where, in the first body and in the measuring tape, materials are used which possess greatly different thermal reactions to temperature variations. It is practical that the measuring tape be attached to the first body solely in the region of the longitudinally-opposite ends of the tape. However, one can also provide points of attachment between the tape ends, in particular in the case of measuring tapes which are very long. This is so because in the case of very long measuring tapes there is the risk that, in a built-in situation wherein the tape is located on a vertically lower side of the first body, the tape""s central part will lift off the first body. This would impair the precision of the measurement.
Practice has shown that it is helpful to have the elastic stretching of the measuring tape amount to at least 30 xcexcm, preferably at least 50 xcexcm, and most preferably about 70 to 100 xcexcm per linear meter of the measuring tape.
One can also conceive of a measuring tape that consists of an article produced by the meter that is drawn from a supply roll. Here again, the elastic stretching of the measuring tape is advantageous in order to stretch the measuring tape to such an extent that unevennesses or undulations possibly caused during winding or unwinding of the tape material will disappear.
Preferably, the measuring tape is made of a metallic material, although synthetic materials can also be considered for the measuring tape. What is essential is that the material for the measuring tape be selected in a manner such that the intentional extension of the measuring tape can be made to occur, at least to the greatest possible extent, if desired, exclusively within the elastic range as opposed to the plastic range. In particular, the material for the measuring tape can be selected in a manner such that the elastic stretch lies in the lower part of the elastic range, far from the limit of elasticity.
Theoretically, the measuring markings can be applied to the measuring tape in any desired form. In principle, there are no limitations to the design of the measuring tape and to the nature of the sensor arrangement""s scanning of the measuring markings. Thus, the measuring markings can be read optically, inductively or capacitively, or else via magnetic resistances or Hall components or according to the principle of eddy-current formation. For instance, the measuring tape can feature an optically readable bar or line pattern or a magnetization pattern with alternating magnetic north and south poles, in order to provide the measuring markings. One can also conceive of providing the measuring tape with a conducting-wire pattern. A preferred form of embodiment of the invention, according to the first aspect, provides for the measuring tape to be equipped, in order to form the measuring markings, with thin zones or breakthroughs in the material, following each other along the length of the tape. If the sensor arrangement used to scan the measuring markings emits an electric or magnetic field and this field is affected by the material of the measuring tape, the thin zones or the breakthroughs of the material represent tape regions in which the permitivity or the permeability of the measuring tape differs from those regions that are not thinner or broken-through zones of the measuring tape. These variations in permitivity or permeability can be captured by the sensor arrangementsxe2x80x94for instance by means of a field plate or a Hall sensor. Thus, one can use a metal screen tape with a relatively high nickel contentxe2x80x94say, up to about 75% wt. Nixe2x80x94in which one inserts (this, provided purely as a numerical example) at a graduation distance of about 1 mm, slits that are about 0.5 mm wide, separated from each other by bridges about 0.5 mm wide.
The measuring markings can comprise a group of markings which follow one another at regular distances along the length of the tape. If the distance between two consecutive markings is known, one can determine the length of the path covered by the second body from the number of the markings passed by the sensor arrangement. If the initial position of the second body is known, one can use the length of the path covered to determine the final position of the second body.
Alternatively or additionally, the measuring markings may comprise a group of reference markings which are designed and/or located on the measuring tape in a manner such thatxe2x80x94even without knowing the initial position of the second body relative to the first bodyxe2x80x94one can make, by passing at the most a few consecutive reference markings, at least an approximate determination of the end position of the second body relative to the first body. Such reference markings are particularly advisable in connection with a track of regularly arranged measuring markings, for the purpose of quickly determining, after a functional or power failure of the sensor arrangement and the consequent loss of positional data on the second body, at least an approximate position of the second body. Here, the so-called distance-coded reference markings were found to be particularly suitable. In that case, pairs of reference markings, adjacent to each other along the length of the tape, feature distances between them which differ for at least a part of the pairs. If the distances between the reference markings of the individual pairs can be captured in table formxe2x80x94e.g., in an electronic memoryxe2x80x94one can directly establish the position of the second body, at least approximately, by the measured distance between two of the adjacent reference markings passed by the sensor arrangement.
In a further development of the first aspect of the invention, it is provided that the first body is an elongated body with a longitudinal axisxe2x80x94in particular, a guide rail of a linear-guide arrangementxe2x80x94and that the measuring tape is applied to the elongated body in the direction of the longitudinal axis.
In order to provide this elongated body, one frequently cuts off a length of material from a material strand, at a cut-off point. For instance, the guide rails for linear-guide arrangements are often produced in the form of strands of a rail several meters long by means of a rolling process, a continuous-extrusion process or a continuous-casting process. Depending on the customer""s wishes, individual lengths of rail are then cut off from these rail strands. If the pieces of rail can only be equipped with a measuring tape after having been cut to size from a rail strand, the procedure and the time delay will be very costly, since the elastic extension of the measuring tape must be carried out for each individual piece of rail. In addition, there may occur mechanical problems, considering that the pieces of rail cut to size are often of different lengths. As a result, the apparatus for clamping the pieces of rail and for stretching the measuring tape must be correspondingly adaptable or adjustable.
In order to simplify the manner of proceeding outlined above, the invention concerns, in a second aspect, a process for producing the arrangement according to the first aspect in which the first body is an elongated body which is cut off from a material strand as a length of material, at a cut-off point. According to the invention, it is provided in this process that a measuring tape be used, extending over a material section of the material strand, which material section is longer, if desired, by a multiple, than the length of material to be cut off. The measuring tape is at first attached to the material strand, under elastic stretching, only in the region of its longitudinally-opposite ends at points of attachment associated with the ends. The measuring tape is then attached to the material strand at additional points of attachment close to the cut-off point, on both sides of the cut-off point in the direction of the longitudinal axis. Next, the material strand together with the measuring tape are cut off between the attachment points which are close to the cut-off points.
With this process, the measuring tape is therefore not attached to the already cut-to-size length of the material strand, but rather before individual lengths are cut off from the material strand, according to the customer""s wishes. In addition, one uses a measuring tape with a length that suffices not only for an individual length but can provide for several lengths, to be cut to size from one and the same material strand.
For instance, rail strands with a length of about 6 m are produced in a rolling mill. Next, one attaches to these rail strands a measuring tape which essentially reaches over the entire length of the respective rail strand. This measuring tape is attached with its tape ends to the rail strand and, in so doing, is stretched within the elastic range. Next, when individual pieces of rail are to be cut to size from this strand of rail, equipped along its entire length with the measuring tape, the measuring tape is additionally attached to the rail strand at strategically selected points, namely, on both sides of each of the selected cut-off points, after which the rail strand, together with the measuring tape, is cut off at the selected cut-off points. The result of this process is that the cut-off pieces of rail each carry a measuring tape which is attached with both its tape ends to the respective rail piece and which is under an elastic tension between its tape ends. Any possibly remaining length of the rail strand is equipped with a measuring tape, namely, the remaining length of the original measuring tape, which is attached at its two tape ends to the rest of the rail strand and is under an elastic tension between its tape ends. In this fashion, one can cut to size several rail pieces from one rail strand, while the procedure of measuring-tape stretching is only required once per rail strand.
In particular, if the strand of material used is a continuous strand, one can use a measuring tape which, while it is longerxe2x80x94in particular, much longerxe2x80x94than an individual length of this material strand that is to be cut off, it only extends over a limited partial length of the material strand.
In this second aspect, the measuring tape is preferably attached to the material strand by welding, particularly spot welding such as, for instance, in a resistance-welding process.
One often wishes to cover the measuring tape by some cover designed to protect it against mechanical factors and aggressive chemicals. In that case, it is theoretically possible to attach the cover only after the individual lengths had been cut to size from the material strand. However, in a preferred further embodiment of the process according to the second aspect of the invention, it is provided that, before the material strand is cut off, a measuring-tape cover is rigidly applied which is separate from the material strand and from the measuring tape and which extends over the length of the material section of the material strand. The measuring-tape cover is cut off at the cut-off point together with the material strand and with the measuring tape and, if desired, is attached to the material strand and/or the measuring tape, before the cut off, close to the cut-off point. This has the following advantage: the material strand with the measuring tape attached to it is often not subdivided immediately into individual lengths, at its production site, but rather is supplied to a post-processing company which places it in storage and at the proper time cuts off the individual lengths, according to the desired customer application. If during this time the measuring tape is left unprotected one cannot exclude the possibility of damage to the measuring tape. However, if the measuring-tape cover is attached to the uncut material strand one can achieve an early and complete encapsulation of the measuring tape which will protect it against subsequent factors capable of occurring during the transportation, warehousing or subsequent processing of the material strand.
For the cover of the measuring tape, a cover tape can be used which is attached, if desired in an essentially continuous manner, to the material strand along the longitudinal edges that run in the direction of the longitudinal axis of the strand. However, other forms of coverage can also be used. For instance, the measuring tape can be built into a longitudinal groove of the material strand and the groove then filled with a hardenable cover mass.
According to a third aspect, the invention concerns an arrangement for determining the relative position of two bodies capable of motion in relation to each other, wherein a first of the two bodies carries measuring markings distributed over a marking range and the second of the two bodies carries a sensor arrangement which responds to the measuring markings, which sensor arrangement travels over the marking range, in the course of relative motion of the two bodies, and in which the measuring markings are covered by a cover tape which is separate from the first body. With a flat side turned towards the first body, the cover tape lies on supporting surfaces of the first body and is attached to the first body, by at least one longitudinal welding seam, along its two longitudinal edges that run in the longitudinal direction of the tape. In this case, the arrangement can be designed in particular in accordance with the previously described first aspect, and can be produced within the framework of the earlier process, according to the second aspect.
It often is impossible to avoid tolerances in the width of the cover tape. Thus, it cannot be excluded that the cover tape will vary in width along its length, even if such variability is small. It can also occur with the longitudinal welding seams that the seams cannot be applied with exact straight-line accuracy, but only with certain deviations from an exact straight-line accuracy. It is possible to apply the longitudinal welding seams directly to the longitudinal edges of the cover tape. However, the two effects discussed earlierxe2x80x94tolerances in the width of the cover tape and lack of straight-line accuracy of the longitudinal welding seamsxe2x80x94can also bring about, at certain points along the cover tape, that to a greater or lesser extent in the welding the cover tape is missed and the weld is applied xe2x80x9cto the air.xe2x80x9d This can cause leaky welding points. In addition, in this fashion one transfers varying amounts of heat to the cover tape along the cover tape. The heat transfer during welding causes thermal stresses in the material of the cover tape, which stresses can manifest themselves in a deformation of the cover tape. Such non-uniform heat inputs can cause an irregular deformation of the cover tape, which can also produce a considerable negative effect on the welding result.
Consequently, a third aspect of the invention is based on the object of providing an improved way of achieving a better welding result when welding the cover tape.
In order to achieve this object, the third aspect of the invention provides that the longitudinal welding seams run at a distance, in the direction crosswise to the direction of the tape length, from the respectively adjacent longitudinal edge of the cover tape and that they form a material fusing zone of the cover tape with the first body, in the region of the supporting surfaces.
Because in this solution, the longitudinal welding seams are applied at a distance from the longitudinal edges of the cover tape, a uniform heat input over the length of the cover tape is ensured. In this fashion, one always melts essentially identical amounts of material of the cover tape and fuses them with the first body. It was found that this promotes a reduction in the deformations of the cover tape caused by the welding. In addition, one avoids the occurrence of leaky welding points.
The measuring markings can be sunk into a relief-like depression of the first body, wherein the cover tape will practically be inserted into the relief-type depression. In this fashion, not only can the measuring markings be protected, but also the cover tape, against the overwhelming majority of mechanical damage.
The cover tape in particular can be inserted into this relief-like depression in a manner such that the outer surface of the cover tape lies approximately flush with the adjoining surface regions of the first body. In this fashion, one achieves an essentially stepless transition between the cover tape and the first body, in a manner such that one generates an outer surface of the structural unit xe2x80x9cfirst body/cover tapexe2x80x9d which is essentially free of unevennesses. If desired, the above would facilitate a perfect sealing of the second body with respect to the first body. This is so because, particularly in the case a of linear-guide arrangement with a slide traveling on a guide rail, the slide is often designed with a seal which is in sealing contact with the guide rail and which prevents the penetration of dirt into the slide and the leakage of lubricant from the slide. By means of an essentially flush insertion of the cover tape into the guide rail one can prevent the occurrence of wear at the seal of the slide, or even the need for modification of the form of sealing.
The welding method according to the third aspect of the invention has a particular advantage in the previously mentioned case, in which the cover tape is inserted in an approximately flush manner into the relief-like depression. In this case, if one were to apply the longitudinal welding seam to the abutting region between the longitudinal edges of the cover tape and the lateral flanks of the relief-like depression, one would run the risk of negatively impacting the welding process due to the gap which could appear between the cover tape and the lateral flanks of the relief-like depression, because of the tolerances in width of the cover tape and/or of the relief-like depression. By applying the longitudinal welding seams as above according to the third aspect of the invention, not in the abutting regions between the cover tape and the relief-like depression but rather towards the middle of the tape, one no longer need take into account such a gap. The cover tape can be produced with greater tolerances in width. At the same time, greater tolerances in manufacture can also be accepted for the relief-like depression. Instead of butt welding, one can weld through the cover tape with the material fusing of the cover tape with the first body occurring in the ideal case entirely in the region of the supporting surfaces of the first body.
A particular advantage is achieved if the relief-like depression is designed as a stepwise depression, and the supporting surfaces for the cover tape are formed by a supporting-step arrangement of the depression. In that case, one can ensure that the measuring markings remain unaffected by the welding process, even if that process does not occur directly at the longitudinal edges of the cover tape but rather is shifted towards its center. This is so because, via the stepwise design of the relief-like depression, one can apply the measuring markings at a point of the depression which is deeper, compared to the supporting-step arrangement, so that they are well protected from the heat generated during welding.
It is preferred that the cover tape be applied to the first body by means of laser welding. This is advantageous because, by means of laser welding, one can achieve very narrow welding seams, a comparatively small melting zone is produced and the melting duration is kept relatively short. As a result, there is no risk of negative effects upon the measuring markings caused by heat generation during laser welding.
Nor are welding processes other than laser welding excluded in principle. Thus, it is conceivable that one can apply the cover tape to the first body alternatively by means of electron-beam welding or plasma welding.
In principle, one could integrally incorporate the measuring markings into the material of the first body, for instance by etching in the depressions, or by impressing magnetic states. However, a further embodiment of the third aspect of the invention provides that the measuring markings are arranged on a markings carrier which is separate from the first body and from the cover tape. This markings carrier can be, for instance, a metal tape into which one incorporates, at regular and/or a periodic intervals, slits designed as measuring markings.
The invention further concerns, according to a fourth aspect, a process for producing an arrangement for determining the relative position of two bodies capable of motion relative to each other, wherein a first of the two bodies carries measuring markings distributed over a marking range and the second of the two bodies carries a sensor arrangement which responds to the measuring markings and which travels the marking range in the course of a relative motion between the two bodies. In this process, the measuring markings are covered by a cover tape, separate from the first body. The cover tape with its flat side turned towards the first body is laid onto supporting surfaces of the first body, and is attached to the first body along the two edges that run along the longitudinal tape direction, by at least one respective longitudinal welding seam. This process is particularly suitable for the production of the arrangement according to the first aspect and/or the third aspect.
According to the invention, it is provided in the process according to the fourth aspect that the longitudinal welding seams are applied at a distance, in the direction crosswise to the longitudinal direction of the tape, from the respectively adjacent longitudinal edge of the unwelded cover tape in a manner such that the welding causes a material fusing of the cover tape with the first body, if desired, exclusively in the region of the supporting surfaces. Here, what had already been stated earlier with respect to the third aspect of the invention essentially applies.
The advantages derived from the fact that one welds at a distance from the longitudinal edges of the cover tape remain operative even if one wishes to cut off the edge strips of the cover tape which remain outside the longitudinal welding seams. This can be done after welding. It is also conceivable that one could already cause a separation of these edge strips during welding, by selecting the welding process in a manner and by keeping the welding energy at a level such that a welding cut results.
According to a fifth aspect, the invention concerns a process for producing an arrangement for determining the relative position of two bodies capable of moving in relation to each other, wherein a first of the two bodies carries measuring markings distributed over a marking range and the second of the two bodies carries a sensor arrangement responding to the measuring marking, the sensor arrangement traveling over the marking range in the course of a relative motion of the two bodies. In this process, the measuring markings are covered by a cover tape, separate from the first body, which is attached to the first body along its two longitudinal edges running in the direction of the tape length, by means of at least one respective longitudinal welding seam. This process is particularly suitable for the production of the arrangement according to the first aspect and/or the third aspect.
This fifth aspect of the invention is based on achieving the object of keeping at a low level the deformations of the cover tape which could be caused by the heat generated during welding.
In this connection, it is proposed according to the invention that longitudinal welding seams adjacent to two different edges-of the cover tape be applied essentially simultaneously. This is so because it was found that, if one first welds along only one of the longitudinal edges, comparatively heavy deformations of the cover tape in its tape plane are to be expected. The resulting warping of the cover tape can have the consequencexe2x80x94particularly if the cover tape is rather long, e.g., several metersxe2x80x94that the cover tape is no longer capable of being welded in a proper fit to the first body. In order to counteract this in the fifth aspect of the invention, one welds simultaneously along both longitudinal edges of the cover tape. In so doing, the tendency towards warping of the cover tape in its tape plane, caused by welding on the one longitudinal edge, is essentially canceled by the tendency towards warping caused by the welding at the other longitudinal edge. As a result, the cover tape remains essentially straight and free of warping.
It is particularly advisable to apply the essentiallyxe2x80x94simultaneouslyxe2x80x94applied longitudinal welding seams in the same welding direction. In so doing, it is practical to apply the welding seams jointly, starting at one and the same lengthwise end of the cover tape.
The longitudinal welding seams which are applied essentially simultaneously can be applied by means of a laser welding apparatus with bifocal optics. Such laser welding devices are available. For instance, they are offered by the firm Haas-Laser GmbH as a variety of high-performance laser devices, such as for instance the one designated Type HL 3006 D.